This invention relates to magnet bases for various magnet type measuring tools and magnet type auxiliary tools.
Various magnetic tools, such as dial gauges and magnet holder type marking-off tools used in machining operations on grinding machines, lathes, milling machines, etc., are used with being magnetically attracted to the tables of these machines, work-pieces, or surface tables. In this connection, there is a tendency that the magnet in the base of such a magnetic tool is made of ferrite material low in cost instead of so-called "alnico-V" series material. However, the ferrite material is low in magnetic flux density and accordingly in magnetic force, when compared with the "alnico-V" series material. In order to overcome this difficulty, a variety of methods have been proposed in the art in which the dimensions of the magnet, i.e. the sectional area of the latter is increased to compensate the insufficient magnetic force due to the low magnetic flux density.
A magnet base of this type has a yoke with a cylindrical hole, and a magnet which is slidably and rotatably inserted into the cylindrical hole of the yoke. In a magnet base using a magnet made of the "alnico-V" series material, the magnet is shaped as shown in FIG. 4. More specifically, the configuration of the sectional area of the magnet is such that the cylindrical hole of the yoke is not completely filled with the magnet; i.e. the configuration of the magnet is such that a cylinder is cut by two parallel planes along its longitudinal axis, so that two cylindrical walls and two parallel walls are left. Accordingly, the two cylindrical walls are slidably rotated in the cylindrical hole of the yoke. This configuration is advantageous in maintaining N and S poles for the magnet. Accordingly, in the case where the "alnico-V" series material which is high in magnetic flux density and tolerable in sectional area design is used to fabricate the magnet, the magnet comes to have the configuration which is obtained by cutting a cylinder as described above without minding the reduction of the sectional area.
On the other hand, in the case where the ferrite material is used to fabricate the magnet, the fact that it is relatively low in magnetic flux density must be taken into account. Accordingly, in designing, it is required to compensate the insufficient magnetic force by making the sectional area of the magnet as large as possible.